The invention relates to a system for automatically steering a tractor in response to an implement position signal generated by global positioning system (GPS) receiver on an implement being pulled by the tractor.
There are known control systems for controlling robotic vehicles pulling trailers. There are also known control systems for controlling heavy trailer truck combinations. However, such systems are not designed to specifically control the location of the trailer. A system is also known for controlling a tractor mounted implement, using GPS measurements, through actuation of the implement itself. However, large actuation forces are required to move large towed implements plowing soil, and in some cases the actuation moves the tractor instead of the implement.
Larsen, W. E., Nielsen, G. A., Tyler, D. A., xe2x80x9cPrecision Navigation with GPS,xe2x80x9d in Computers and Electronics in Agriculture, Vol. 11, 1995, pp. 85-95, suggest that GPS can be used to navigate a tractor and implement along a predetermined path, and appears to describe a model which, based on the geometry of the tractor and implement, determines or calculates the position of the implement. However, in certain situation, using a model to calculate implement position can produce erroneous implement position information, such as when a tractor and an implement are operating on a hillside.
Smith, L. A., Schafer, R. L. and Young, R. E., in xe2x80x9cControl Algorithms for Tractor-Implement Guidance,xe2x80x9d Transactions of the ASAE, Vol. 28, No. 2, March-April 1985, pp. 415-419 describe control algorithms for guiding a tractor-implement combination. However, these algorithms are based on a xe2x80x9cconstant-turnxe2x80x9d geometric relationship, and, in the aforesaid hillside situation, using such a geometric relationship can also produce erroneous implement position information.
U.S. Pat. No. 5,764,511, issued Jun. 9, 1998 to Henderson, discloses a system and method for controlling the slope of cut of a work implement moved across a terrain by a vehicle. However, this system does not control the steering of the vehicle.
Accordingly, it is desired to provide a control system designed to accurately control the position of an implement towed by a tractor.
A further object of the invention is to provide such a system which utilizes GPS technology.
Another object of the invention is to provide such a system which uses differential carrier-phase GPS measurements on both the tractor and towed implement.
Another object of the invention is to provide such a system wherein control is accomplished through the steering actuation of the tractor.
These and other objects are achieved by the present invention, wherein a control system is provided for a work vehicle towing a towed implement. The vehicle has a steering system including a steering actuator for steering steerable wheels. The control system includes a steering angle sensor for generating a steering angle signal representing an angular position of the steerable wheels, and an implement GPS antenna and receiver on the implement for generating implement position data. The control system also includes a fixed land-based GPS antenna and receiver for generating reference position data. A set of vehicle GPS antennas are mounted on the vehicle, and a vehicle GPS receiver is coupled to one of the vehicle GPS antennas and generates vehicle position data. A vehicle wireless receiver receives transmitted reference position data. A vector unit coupled to the vehicle GPS antennas generates a vehicle attitude signal. A first processor generates an implement position signal as a function of the implement position data and the reference position data. A second processor generates a vehicle position signal as a function of the vehicle position data and the reference position data. An inverse kinematics processor is coupled to the first and second processors and to the vector unit, and generates an implement angle signal as a function of the implement position data, the vehicle position data and the vehicle attitude signal. A control processor is coupled to the first and second processors, to the vector unit, to the an inverse kinematics processor, to the steering angle sensor, and generates a steering control signal as a function of the implement position data, the vehicle position data and the vehicle attitude signal, the implement angle signal, the steering angle signal and a stored desired implement position signal (such as a pair of east/west coordinates). The steering actuator receives the steering control signal and steers the steerable wheels in response thereto.